The present disclosure relates generally to a turbomachine, and, more particularly, to a face seal assembly including a plurality of isolated hydrostatic ports and a method of operating such a face seal assembly in the turbomachine.
Turbomachines generally include compressors, turbines, and a rotor, such as, a shaft or a drum, which support turbomachine blades. For example, the turbomachine blades may be arranged in stages along the rotor. The turbomachine may further include various seals to reduce a leakage flow of a process fluid between various components of the turbomachine. For example, the turbomachine may include a face seal assembly configured to reduce the leakage flow of the process fluid from a high-pressure cavity to a low-pressure cavity. Typically, such a face seal assembly may include a sealing ring slidably coupled to the housing and disposed proximate to a rotor. During stationary condition, such as, zero speed or low-speed operating condition, sealing faces of both the sealing ring and the rotor are in contact with each other. While, during normal operating condition, a fluid-film of a pressurized fluid may separate the sealing faces from each other and prevent wear due to friction. The fluid-film may further reduce the leakage flow of the process fluid there between the sealing faces.
The face seal assembly, for example, a hydrodynamic face seal assembly typically operates with a thin fluid-film (i.e., about 2 microns to about 10 microns). The sealing faces for such a face seal assembly needs to have a high degree of flatness, tight assembly tolerance, and small thermal deformation for operating with the thin fluid-film. These requirements of the sealing faces may become further difficult to maintain with increasing diameter of the sealing ring and the rotor. Specifically, the cost of machining the sealing faces of a large diameter (e.g., 0.5 meters or larger) sealing ring and the rotor to a high degree of flatness (e.g., less than 5 microns of the fluid-film thickness) is very high. Further, during start-up condition, the sealing faces may rub against each other resulting in wearing the sealing faces. The sealing faces may further deform/cone either inwardly or outwardly due to thermal loads and/or pressure loads.
The face seal assembly, for example, a radial Rayleigh step hydrostatic face seal assembly typically operate with a fluid-film thickness larger than a fluid-film thickness of a hydrodynamic face seal. Such a face seal assembly may result in changing the fluid-film thickness along the radial direction. However, a fluid-film stiffness and reliable operation of such a face seal assembly depends on the coning deformation of the sealing faces. The face seal assembly, for example, an orifice-compensated hydrostatic face seal assembly has a plurality of orifices for delivering a high-pressure fluid from a high-pressure cavity to the fluid-film to separate the sealing faces and generate a thick fluid-film (i.e., about 25 microns to about 100 microns). However, the orifice-compensated hydrostatic face seal assembly is inherently associated with a lower fluid-film stiffness. The face seal assembly, for example, a barrier fluid hydrostatic face seal assembly is used to inject a barrier fluid using a plurality of pockets along a face seal clearance and prevent a leakage flow of a process fluid. Typically, such a barrier fluid hydrostatic face seal assembly includes a groove, which extends along a circumferential direction of the sealing face and connects the plurality of pockets to each other. However, the groove and the connected pockets reduce the ability of such a face seal assembly to adjust any angular misalignment of the rotor.
Accordingly, there is a need for an enhanced face seal assembly for a turbomachine and an associated method for operating such a face seal assembly to provide a high fluid-film stiffness at a relatively thick fluid-film such that the fluid-film stiffness is less sensitive to rotational speeds, deformations of the sealing faces, and angular misalignments of the rotor.